In the polymerization of the free diamine, 4,4'-diaminodiphenic acid (DPA) with terephthaloyl chloride by standard procedures, e.g., in an alkylamide solvent at low temperature, low molecular weight polymer, inherent viscosity &lt;1.5 is obtained. When the dihydrochloride of DPA is combined with a solvent, such as dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP), it dissolves in about one hour because the basicity of the solvent (present in large excess), though low, enables it to dissociate to free amine. Subsequent reaction with terephthaloyl chloride again gives low molecular weight polymer. This behavior is believed to relate to the unusual nature of DPA, namely, the fact that it is a bis(aminoacid). As such, the compound has a propensity to form internal salt links with itself which are highly insolubilizing. Even storage of DPA in the free diamine state for short periods while not precluding dissolution, can deactivate some of the amino groups with regard to their ability to react with terephthaloyl chloride, thus effectively unbalancing stoichiometry and limiting polymer molecular weight. The process of the present invention provides a procedure to overcome this problem.